Circuit cards are often tested to ensure that the circuitry within the card and the components on the card are present and functional. If a circuit card includes a connector, it is desirable to also test the connector. If a circuit card is tested without testing the connector the circuit card may successfully pass the test while not having the connector installed or while having a non-functional connector installed.
Circuit cards can be tested using a test fixture 100 as shown in FIG. 1, for example. The test fixture 100 includes a first plate 110 having locating pins 112, 114. The locating pins 112, 114 are located corresponding to the location of apertures in a circuit card 120. The locating pins 112, 114 are used to properly position the circuit card 120. The circuit card 120 shown in FIG. 1 is aligned in the test fixture 100 with the locating pins 112, 114 protruding through the apertures of the circuit card 120.
A probe block 130 including probes 116 is attached to the first plate 110. A backer gate 140 includes probes 142 and posts 144. The probes 142, 116 contact the circuit card 120 to test components on the circuit card 120 or the circuitry of the circuit card 120. Each probe 142, 116 contacts a designated signal on the circuit card 120. The posts 144 prevent the force of the probes 116 of the probe block 130 from bowing the circuit card 120.
Circuit cards 120 often include connectors 150 mounted on the circuit cards 120 as shown in FIG. 1. The probes 142, 116 can be used to test components on or the circuitry of the circuit card 120 but will not test the connector 150. To test the connector 150, a side access unit 160 engages the connector 150 with side probes 162. When the side probes 162 engage the connector 150, the side probes assert a force in the "A" direction upon the connector 150. Because the connector 150 is mounted on the circuit card 120, the force in the "A" direction is applied indirectly to the circuit card 120.
The number of side probes 162 needed to conduct a test increases as the number of connectors 150 on a circuit card 120 increases and as the number of pins on a connector 150 increases. The force in the "A" direction increases as the number of side probes 162 used to interconnect with the connector 150 increases.
The lateral motion of the circuit card 120 due to the force applied by the side probes 162 is opposed by the locating pins 112, 114 which are used to position the circuit card 120. As the number of side probes 162 increases, however, the force may become excessive and the locating pins 112, 114 may bend or the apertures in the circuit card 120 may elongate, thus allowing the circuit card 120 to move laterally. This results in damaged locating pins 112, 114 or a damaged circuit card 120. If the probes 142, 116 were in contact with the circuit card 120 when the side probes 162 caused the circuit card 120 to move laterally, the probes 142, 116 may also be bent and damaged.
In addition to costs resulting from the damage to the locating pins 112, 114, to the probes 116, 142, and to the circuit card 120, lateral movement of the circuit card 120 will result in the circuit card 120 being incorrectly positioned. The probes 116, 142 are located to contact signals on the circuit card 120. Successful contact with the signals on the circuit card 120 depends on the circuit card 120 being in a desired location. When the circuit card 120 is incorrectly positioned, the probes 116, 142 may not contact their designated signals on the circuit card 120. The probes 116, 142 may contact an incorrect signal or no signal. This may result in a test failure of a circuit card 120 that is properly functional or result in test failures that are erroneously attributed to a misaligned circuit card 120.
An edge block 170 as shown in FIG. 1 may be used to offset the force in the "A" direction applied by the side probes 162. The use of an edge block 170 is effective when the distance "B", which is the length of the circuit card 120 that extends past the locating pin 114, equals the distance between the locating pin 114 and the edge block 170. Due to manufacturing tolerances, however, the distance "B" on circuit cards 120 is inconsistent. The distance "B" typically varies by .+-.0.51 mm (.+-.20 mils).
If the distance "B" is less than the distance from the locating pin 114 to the edge block 170, the force in the "A" direction will not be offset by the edge block 170 until the locating pins 112, 114 have bent or the apertures in the circuit card 120 have elongated. If the distance "B" is greater than the distance from the locating pin 114 to the edge block 170, the circuit card 120 will not fit on the first plate 110.
To overcome the shortcomings of conventional circuit card testing, a new test apparatus is provided. An object of the present invention is to provide an apparatus for preventing the lateral movement of a circuit card. A related object is to provide an improved test apparatus for testing circuit cards by preventing lateral motion of the circuit card during testing. Another object of the present invention is to prevent lateral motion of a circuit card during testing when the location of the end of the circuit card is variable.